Electrical apparatus, such as motors and turbine generators, occasionally overheat due to shorts or other malfunctions. The longer the overheating continues the more damage is done to the apparatus. A malfunction detected immediately may mean only a quick repair but if the overheating continues, the entire machine may be damaged.
Large rotating electrical apparatus is usually cooled with a hydrogen gas stream. The organic compounds in the apparatus are first to be affected by the overheating and they decompose to form particles which enter the gas stream. Monitors then detect particles in the gas stream and sound a warning or shut down the apparatus when too many particles are detected.
Descriptions of such monitors and how they function may be found in U.S. Pat. No. 3,427,880 titled "Overheating Detector For Gas Cooled Electrical Machine" and in U.S. Pat. No. 3,573,460 titled "Ion Chamber For Submicron Particles." Another monitor, "The Condensation Nuclei Detector," is described by F. W. VanLuik, Jr. and R. E. Rippere, in an article titled "Condensation Nuclei, A New Technique For Gas Analysis," in Analytical Chemistry 34, 1617 (1962) and by G. F. Skala, in an article titled "A New Instrument For The Continuous Detection Of Condensation Nuclei," in Analytical Chemistry 35, 702 (1963).
As U.S. Pat. Nos. 3,427,880 and 3,807,218, and the hereinbefore-cited cross-referenced applications disclose, special coatings may be applied to the apparatus which decompose to form detectable particles (i.e, thermoparticulate) at a lower temperature than the usual organic compounds found in the apparatus. However, merely knowing that an area in the generator is being overheated may not be enough information on which to base a decision to shut down the generator. Since shutting down a generator means the loss of the electricity which would have been generated plus the cost of inspecting, disassembling, and reassembling the generator, such decisions are not made lightly.